Two-dimensional pulse counting or registering tube



1954 A. M. SKELLETT ,9

TWO-DIMENSIONAL PULSE COUNTING 0R REGISTERING TUBE Filed Feb. 24, 1950 2 Sheets-Sheet 1 P0456 INPUT 'Jdl/KCE.

I ALBERT M. SKELLETT INVENTOR.

Nov. 30, 1954 A. M. SKELLETT 2,695,974

TWO-DIMENSIQNAL PULSE COUNTING OR REGISTERING TUBE Filed Feb. 24, 1950 2 Sheets-Sheet 2 l .IIH

T ALBERT /"l. SKELLETT IN VEN TOR.

United States Patent 2,695,974 Patented Nov. 30, 1954 ice TWO-DIMENSIONAL PULSE COUNTING R REGISTERING TUBE Albert M. Skellett, Madison, N. J., assignor to National Union Radio Corporation, Orange, N. .11, a corporation of Delaware Application February 24, 1950, Serial N 0. 146,029

16 Claims. (Cl. 31512) This invention relates to registering and counting tubes and more particularly to such tubes as employ a deflectable electron beam.

Heretofore, various forms of counting or pulse registering tubes have been devised wherein a cathode-ray beam is deflected to any one of a series of successive positions and held at the deflected position until the reception of a succeeding pulse. A typical example of such tube is disclosed in my application Serial No. 35,025, filed June 24, 1948, and issued June 10, 1950, as Patent Number 2,599,949.

The present invention has for one of its principal objects the provision of a pulse counting or registering tube of the deflectable beam type, wherein the number of pulse registering or counting positions is greatly increased.

Another object is to provide a pulse registering and counting tube of the deflectable cathode-ray beam kind, wherein the beam is subjected to deflection in coordinate directions to increase the counting capacity of the tube.

A feature of the invention relates to a pulse counting or registering tube of the deflectable cathode-ray beam kind having a two-dimensional target or a plurality of targets arranged in coordinate rows, together with cooperating beam holding and deflecting electrodes for moving the beam in coordinate directions over the target or targets and holding it at the target corresponding to the number of received pulses.

Another feature relates to a novel beam holding arrangement for pulse counting or registering systems of the cathode-ray tube type.

A further feature relates to an improved system of control circuits for a cathode-ray beam tube whereby the beam can be moved to any desired point in a series of successive rows of positions and held at the selected position in accordance with the number of pulses to be counted.

A further feature relates to a novel beam holding arrangement for pulse counting or registering tubes of the type employing a cathode-ray beam arranged for coordinate deflections, with one direction of deflection controlled by the group number of received pulses and the other direction of deflection being controlled by the individual number in the group.

A further feature relates to the automatic switching of a cathode-ray beam from one level of a target or series of targets to a different level of targets.

A still further feature relates to the novel organization, arrangement and relative location and interconnection of parts which cooperate to provide an improved pulse counting or registering tube.

Other features and advantages not particularly enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims.

In a drawing,

Fig. l is a schematic diagram of the novel counting tube and associated control circuits according to the invention.

Fig. 2 is an enlarged view of certain of the electrodes of the tube of Fig. 1, looking in the direction of the arrows.

Fig. 3 represents a modification of the tube of Fig. 1.

In the conventional pulse counting tube, it has been the practice to provide a cathode-ray beam which is stepped in successive steps by the receipt of successive pulses. After the cessation of the pulse series, the beam is automatically held in its deflected position pending the re- 8 ceipt of either a restoring pulse or further pulses which are to be added to the first series. Cooperating with the beam there has been provided a row of targets upon which the beam impinges. In general, these prior tubes have had the targets arranged in a single linear row and in that sense the tube has been single dimensional. In other words, the cathode-ray beam merely sweeps in one direction across the targets. The present invention provides a tube and associated circuits whereby the counting or stepping function of the cathode-ray beam can take place in two different directions. This therefore greatly increases the pulse counting or registering capacity of the tube.

Referring to Fig. l of the drawing, the tube according to the invention, comprises any well-known evacuated enclosing envelope 10, having a neck portion 11, wherein is mounted any well-known form of electron gun. This gun may comprise for example the usual indirectly heated cathode 12, a first electron accelerating anode 13, and a second and higher voltage, electron accelerating anode 14. These electrodes cooperate to produce a sharply focussed beam 15 of electrons. Mounted in the path of the beam 15 are two sets of deflecting elements for deflecting the beam in mutually perpendicular or coordinate directions. The first set may comprise deflector plates 16, 17, for controlling the deflection of the beam in a horizontal plane. The second set of elements may comprise deflector plates 18, 19, for controlling the deflection of the beam in a vertical plane. It will be understood of course, that the terms horizontal and vertical are relative and are intended to cover any coordinate deflection of the beam. If desired, the interior wall of the tube can be provided with the usual conductive coating 20 of Aquadag which acts as a final accelerating anode, and prevents detrimental wall chargings.

The opposite end of tube 10 has an enlarged section 21, and sealed through the left-hand end of section 21 are a series of lead-in and electrode support wires 22, 23, 24, 25, 26, 27. Connected to the wire 22 is a beam holding grid electrode 28 consisting of a plurality of equally spaced horizontal conductive wires or strips 29 (see Fig. 2), these wires being welded or otherwise fastened at their ends to metal frame members 30, 31. Connected to wire 26 is another beam holding grid 32 comprising a series of parallel spaced wires 33, which are welded or otherwise fastened at their ends to the conductive frame members 34, 35. Preferably, although not necessarily, the inter-spacing between the wires 29 is equal to the inter-spacing between the wires 33, and preferably, although not necessarily, each grid has the same number of grid wires. Merely for purposes of illustration, it will be assumed that the grid 28 has nine equally spaced wires 29, and the grid 32 also has nine equally spaced wires 33.

These grids are so mounted that the wires 29 are horizontally located, that is they are parallel to the deflecting field which is set up between plates 16 and 17. On the other hand, the grid 32 is mounted so that the wires 33 extend perpendicularly to the wires 29. Connected to wire 25 is a secondary electron suppressor grid 36. This grid may be of any fine mesh construction but preferably it is of a mesh with the vertical and horizontal wires of the mesh in alignment respectively with the wires 29 and 33. Connected to the wire 24 is a target electrode 37, which may be in the form of a metal plate having its surface facing the electron gun coated with any well-known electron responsive fluorescent material. Mounted in coplanar relation with the target 37 but slightly spaced therefrom is another similar but narrow or strip-like target 38 which is connected to wire 23. Likewise, mounted adjacent the upper edge of target 37 is an additional narrow or strip-like target 39 which is connected to wire 27. It will be observed that the target 39 has the same length as the width of target 37, but the target 38 has a length which is equal to the combined height of target 37 and the width of target 39. Likewise, it will be observed that the grid 28 is of a sufficient length so that it extends at opposite ends beyond the edge of target 37 and beyond the edge of target 38. Likewise, the grid 32 is of a sufficient length so that it extends at opposite ends beyond the edge of target 37 and beyond the edge of target 39. Thus the target 37 may be considered as made up of one hundred equal squares or target elements consisting of ten horizontally arranged squares and ten vertical rows of such squares.

The target 38 is a fly-back control target whose function is to automatically restore the beam to the beginning of the next row of squares upon the receipt of the tenth pulse in each series. The target 39 is also a fly-back control target, the function of which is to automatically restore the beam to the zero square after the reception of one hundred pulses, as will be described hereinbelow. It will be understood, of course, that the grids 28, 32 and 36, are spaced apart a predetermined distance from each other alongthe tube axis, and the plane of the targets 37, 38 and 39 is likewise spaced a suitable distance from the grid 36. The suppressor grid 36 is preferably biassed or so volts negative with respect to the target 37. The target 37 may be maintained at approximately 300 volts positive; the suppressor grid 36 may be at approximately 275 volts positive; and the targets 38 and 39 may be each at approximately 225 volts positive. In .all these cases, the positive voltage is of course refer-red to ground. Thus the grid 36 serves as a suppressor grid for the secondaries emitted from target 37, but it serves the opposite ,pur- ,pose for the two target electrodes 38 and 39. In other words, grid 36 will draw-off the secondary electrons from targets 38 and 39. but will suppress the secondary electrons from target 37.

As will be described hereinbelow, the grid 32 functions to hold the deflected electron beam in its horizontally deflected position in accordance with the number of pulses that are received. Likewise, the grid 28 functions as a holding electrode to hold the deflected beam in its vertically deflected position in accordance with the number of pulses received. The horizontal deflector plates 16 and 17 are connected to the anodes or output circuits of a pair of push-pull connected grid-controlled vacuum 'tubes 40, 4'1. Likewise, the vertical deflecting plates 18 and 19 are connected to .the anodes or output circuits of another pair of push-pull connected grid-controlled vacuum tubes 42, 43. The system is arranged so that the tubes respond .to negative pulses applied to the input terminals 44, 45, which are connected to a suitable pulse source '46. These input pulses are impressed through a coupling condenser 46a and in push-pull relation 'on the control grids 4-7, 48, by means of the input resistors 49, 50, the "cathodes '51, 52, of these tubes being returned to :ground through the bias resistor 53. The common point 5'4 of the input circuit is returned to ground through an adjustablebias res'istoror potentiometer 55. The resistor 55 may be connected in series with another resistor 56 and thence to the positive terminal 57 of a suitable source of direct current plate power supply, for example positive three hundred volts. This terminal 57 is also-connected .through the plate .load resistors '58, 59, .to .the respective anodes 60, 61, of tubes and 41. The horizontal deflecting plates 16, 17, are directly connected to the .re- 'spective anodes 6d and 61. The tubes 40 and 41 thusact as agpush-pull amplifier for the negative input pulses. The 'bearnholdinggrid '32 is connected directly to the control grid 47, While the'beam holding grid 28is .connectedvdirectly to the .control grid 62. The tubes 42 and are likewise connected to form a push-pull amplifier with the control jgrids 62 and 63 connected through respectivelinput resistors .64, 65, and thence toground through .the adjustable resistor or potentiometer6'6. The cathodes 67, 68, are also returned to ground through .the bias resistor '69. The resistor '66 is-connected in series withanother resistor '70 'audthence to the positive power supply :terminalf57'which is also connected through respective plate l'oadresistors 71, '72, to the respective anodes "73, 74. The anodes "73 and 74 are-connected directly-to-the vertical deflectingplates 18, 19.

Tubes 4Iland 41 are biassed by means of potentiometer so that in the absence of negative pulses .from source 46, a potential is developed across the deflector plates 16 and 17 such that the beam 15 strikes or .impinges upon the lower'left-haud cornerof the.target,37, or the #9 element. in response .to the first-negative pulse from the source -46, there .is .developed across plates .16 and 17,.a voltage suflicienhto deflect-the beam one'square to the right so thatit then impinges upon the #1 .element of target .37. :Uponthe cessation of this first .negative pulse, there would .be a tendency for the.beam to return to its initial Zero position. :Since the amplitude of the first :pulse .is .suflicient totcause .the beam to pass over the first vertical wire of grid 32 on to #1 element of the target, if the beam should attempt to return to its initial Zero position, it will again be intercepted by this first vertical grid wire and some of the beam current will therefore flow to the grid 32. This current will drive the potential of grid 32 negative, and since this negative potential is also applied directly to the control grids 47 and 48, the resultant potential developed across plates 16 and '17 will be just enough to counter-balance the tendency of the beam to return to its initial Zero position. Thus the beam stays put on #1 target. Upon .the receipt of succeeding negative pulses of the series, the beam is likewise stepped to the right as seen in Fig. .2, andonce it is deflected by the appropriate number of pulses to the corresponding numbered square of target 37, it will stay put 'by the same action as above described. In other words, for all horizontal settings of .the beam in response to a series of negative pulses up to nine, the feedback to the grids 47, 4.8, by reason of the tendency of the .beam to fall back and thus intercept a vertical grid wire, will result in a holding of the beam in a position adjacent to that particular vertical grid wire. Thus a series of negative pulses applied to terminals 44 and 45 will step the beam progressively to the right, as seen in Fig. 2, towards target 38. :If however, fewer than ten pulses have been received, for example five, the beam will be stopped on the #5 element of the target 37 and will remain there indefinitely.

In accordance with the invention, if more than nine consecutive pulses are received the beam is automatically cause to fly-back, and during the fly-back it is vertically deflected to the next vertical row of elements on the target 37, for example on :the tenth pulse the beam is caused ,to automatically fly-back .and is vertically deflected so that it comes to rest on the #10 element and remains there until succeedingzpulses are received. In order to hold the beam on the particular vertical level of squares determined by the number of received pulses, the tubes 42 and 43 provide a similar holding circuit for the vertical deiflection 0f the beam, "the holding electrode in this case being formed by the grid wires 29. The action of these gridWires-in holding the beam in its vertically stepped position is the same .as that described above in connection with theho'lding action of the grid wires 33.

In order to control the automatic fly-back of the beam upon the receipt .of each tenth pulse, there is provided a grid-controlled gaseous tube or Thyratron 75, the control grid 76 of which is connected through a suitable coupling condenser 77, to the target 38. The cathode 78 of the 'Thyratron' is connected to ground through the current limiting resistor 79, and the control grid 76 is connected through a resistor 80 to a negative terminal 81 on'the direct current power supply source, which terminal is slightly negative with respect to ground, for example minus ,three volts. The anode 82 is connected through the series resistors ;83, 84, to the positive direct current -terminal 57 of thepower supply source.

Normally :the voltages applied to the various electrodes of tube 75 are suchas to prevent that tube from becoming plate current conductive. However, when the beam 15 impinges on the target '38 as a result vof the receipt of a tenth pulse, the target 38 emits secondary electrons so that the .potential of target 38 becomes positive by a few volts. This positive voltage is then ,applied to grid 76, and triggers the tube 75 into the fired condition causing plate current to flow. As a result of this, the potential of anode 82 drops suddenly, producing -a .negative pulse, and this negative pulse is applied through condenser 85 to the grid 48. This negative pulse applied to grid 48, changes the potential across plates -16 and 17, whereby the beam 15 ,returns substantially instantaneously to the initial position at the left-hand side of target 37. However, at the same time, the last-mentioned pulse sets up across the resistance network :83, 8'4, a smaller negative pulse which is applied through condenser 86 to the control grid 62. The application of this pulse to the grid -62 results in a change in ithe deflector :potential on plates 1-8, 19, to cause the beam to step up vertically to the second row of elements on target 37 where it registers with the #10 square. As above :mentioned, the beam is held between the first :and second wires 29 and is prevented from migrating iback to :the #0 element. As the succeeding pulses areapplied to 'therterminals .44 and '45, the beam is rcolfrespondingly stepped rhorizontally vacross the sec- 0nd tier of elementson target 37. If the number of succeeding pulses is ten or more, the beam again strikes the target 38 and it automatically fiys back and during this fly-back it is stepped up vertically to the next tier of elements on the target 37.

A similar action takes place depending upon the total number of pulses that are received. In the particular arrangement disclosed, the device is arranged to count up to one hundred pulses. On the receipt of the one hundredth pulse, the beam will fly-back horizontally, and will be stepped up vertically, in the manner above, described, so that it strikes the target 39. The target 39 is connected through a suitable condenser 87 to the control grid 88 of a grid-controlled gaseous conduction tube or Thyratron 89 which may be similar to the tube 75. The control grid 88 of this tube is connected through a suitablable resistor 90 to the negative biassing terminal 81, and the cathode 91 is returned to ground through the limiting resistor 92. the anode 93 being connected through the series resistor 94 to the positive terminal 57. When the beam strikes the target 39, the latter becomes secondary emissive and goes positive by a few volts, thus triggering the Thyratron 89 to firing condition and developing a pulse at its anode 93 which is coupled through condenser 95 to the control grid 63. As a result of this action, the potential across plates 18 and 19 is changed, causing the beam to automatically return to its initial position where it impinges on the #0 element at the lower left-hand corner of target 37. The apparatus is thus in condition to count the next series of one hundred pulses. If desired, the targets 38 and 39 can be connected to suitable respective indicators or registers which therefore record each complete series of ten pulses and each complete series of one hundred pulses.

In order to enhance the secondary emission characteristics of the targets 38 and 39, these targets are connected through respective resistors 96, 97, to a terminal 98 on the direct current power supply which is less positive, for example 50 volts less than the potential applied to grid 36. It will be understood, of course, that the invention is not limited to the production of the automatic fiy-back pulses by secondary emission from the targets 38, 39. These two targets can, if desired, be biassed positively with respect to the grid 36 so that when the beam impinges thereon, negative pulses are derived respectively from these targets, which pulses are derived of course from the primary emission of the beam impinging thereon. rangement such as buffer tube stages of amplification, these negative pulses can be converted into positive pulses which are then applied to the grids 76 and 88. If the main target 37 is coated with a fluorescent material, the actual position of the beam can be visually observed by the fluorescence from the particular square upon which the beam is held.

While in the foregoing, the target 37 has been disclosed as a single continuous plate with a single lead-in wire 24 it will be understood that this plate may consist of a series of individual. smaller targets, for example it may consist of ten separate rows of ten separate targets in each row corresponding to the elements 099, and each target may be provided with a separate lead-in for connection to respective registers (not shown).

While one particular organization of apparatus has been disclosed herein, it will be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. Pulse counting apparatus, comprising a cathoderay tube having means to develop a beam of electrons, target means upon which said beam impinges and including a series of target elements arranged in horizontal and vertical rows, beam deflector elements for deflecting the beam in mutually perpendicular directions with respect to said target elements, a first beam fly-back control electrode common to all horizontal rows and upon which the beam impinges after leaving any horizontal row of target elements, a second beam fiy-back control electrode common to all vertical rows and upon which the beam impinges after leaving the last target element of the last horizontal row, means to energize said deflector elements by a series of successive received pulses to cause the beam to step successively across all By any well-known pulse-inverting artargets in the first horizontal row before proceeding to the next horizontal row and for thereafter causing the beam to stop at a correspcnding particular target element in said next horizontal row, and means to continuously hold the beam on said particular target element as determined by the total number of successive pulses.

2. Apparatus of the type described, comprising a cathode-ray tube having means to develop a beam of electrons, a plurality of target elements arranged in more than two vertical rows and in more than two horizontal rows with x target elements in each row, means to step the beam from the first target element in a row to all the succeeding target elements in that row until x pulses have been received and before proceeding to the next row; means including a separate target electrode common to all said rows; automatically effective only when x pulses have been received to move the beam to the first target element in the next horizontal row, said stepping means being effective to step the beam successively in accordance with the total number of successive pulses to the appropriate row and to the selected target in that row, and means to continuously hold the beam on the selected target element to which it has been moved.

3. Apparatus of the type described, comprising a cathode-ray tube having means to develop a beam of electrons, a plurality of target elements arranged in vertical and horizontal rows with x target elements in each horizontal row and with y horizontal rows, where x and y are greater than two means'to step the beam from one target element in a row to the succeeding target elements in that row until "x pulses have been received, means automatically efiective only after x pulses have been received to move the beam to the first target element in the next horizontal row, said stepping means being effective to step the beam in response to the total number of successive received pulses to the appropriate row and then to a selected target in said row, means automatically effective when a number of pulses equal to the product xy have been received to move the beam back to the first target element of the first horizontal row, and means to continuously hold the beam on the se lected target element to which it has been stepped.

4. A pulse counting electron tube, comprising an electron gun having means to develop a beam of electrons, a target having a plurality of horizontal rows of target elements and a plurality of vertical rows of target elements upon which the beam successively impinges in response to the number of received pulses to be counted, said beam traversing all targets in one horizontal row before proceeding to the next horizontal row, an automatic horizontal fly-back control electrode adjacent the vertical edges of all said targets, another automatic vertical fly-back control electrode adjacent the horizontal edges of all said targets, and first and second beam-holding electrodes located between said gun and targets, one beam-holding electrode acting to continuously hold the beam in a horizontally-stepped position and the other beam-holding electrode acting to hold the beam in a vertically-stepped position.

An electron tube according to claim 4, in which a secondary emission suppressor electrode is located between the said holding electrodes and the target.

6. An electron tube according to claim 4, in which said target is provided with a fluorescent coating on the side facing the electron gun to give a visual indication of the held position of the beam.

7. Apparatus of the type described, comprising a cathode-ray tube having an electron gun to develop a focussed beam of electrons, horizontal beam-deflecting means, vertical beam-deflecting means, a target having a series of target elements in coordinate horizontal and vertical rows each row being allotted to a sub-group of received pulses to be counted and there being more than two target elements in each horizontal row and in each vertical row, beam-holding means for continuously holding the beam on any target element to which it has been deflected by the pulses to be counted and after the cessation of said pulses, means to apply the pulses to control the horizontal deflection of the beam, means automatically effective only upon the receipt of a complete sub-group of pulses representing the total number of targets in each horizontal row to step the beam to a succeeding horizontal row of target elements, and means effective when all the target elements have been successively impinged enema/7,4

7 mn by ssaid tibeam :for :automatically restoring tthe beam :to the :first target element ofathe-first horizontal .row.

:8. :Pulse'counting apparatus, vcomprising 'a:cathode-ra'y tube having :an'electron gun'to develop a:focussed-cath aQd-I3Y beam, a-target upouwhichzthe beam impinges and :having target-elements arranged in successive horizontal rows, a:horizontal beam 'defiectorga vertical beam .deflector, a'first grid controlled-txacuumtube having the output connected to said 1 horizontal :beam deflector, another; grid-controlled vacuum tube-having its; output con- :nected tosaidyertical beam .pdeflector, .a horizontal flyback control electrode, .means tozapply the pulses to be :counted 'to the input of said first vacuum tube, 'means connectedtmsaid fly-backelectrode and to saidfirst vac- ;uum-tubestodevelop a horizontal :fly-back voltage, means to apply said horizontal fly-back voltage -to said hori- :Zontal beam deflector, :and means to derive 'from said horizontal -fly-back voltage a stepping voltage for anltomaticallystepping the beam *from one horizontal row of targetrelements -to the-next horizontal row of target elements.

9. Pulse counting :apparatus, comprising a cathoderay'tubehavingan electron gun :to develop :a focussed cathode-ray .beam, a target upon which the beam impinges and having-target elementsarranged in successive rhorizontal :rows, a horizontal beam deflector, :a vertical ,bearn deflector, .a first grid-controlled vacuum tube hav- -ing :the output connected to 'said 'horizontal'beam deflector, zanother grid-controlled vacuum tube "having its output connected to said vertical beam deflector, a horizontal fly-back control electrode, a vertical "fly-back control electrode,-means to apply the pulses to be counted ,to.the inputof said first vacuum tube, means {connected to .said horizontal fly-back electrode and "to said first 'vacuum tube to develop a horizontal fly-back voltage, .means to apply said horizontal fly-back voltage'to 'said horizontal beam deflector, means to 'derive from said ,horizontal .fly-back voltage a stepping voltage 'for automatically stepping the beam from one horizontal row ioftarget elements to the next horizontal row of target elements, and means connectedto said vertical fiy-back electrodeand tothe :input of said second vacuum tube to develop ,a vertical fly-back voltage for "restoring the beam .to the first target element of the first'horizontal .row.

10. Apparatus according to claim 8, in which said means connected to said fly-backelectrode for developingsaid fly-back voltage includes a grid-controlled gaseous conduction tube :having its control grid connected to. said fly-back controlelectrode and its anode connected .to thecontrol grid of said first vacuumtube.

.11. Apparatus according to claim 10, in which said fly-back controlelectrode is negatively biassed to act as a.-se,condary electron emitter, and said means connected to said .fly-back electrode -for developing said fly-back voltage includesa grid-controlled gaseous Conductiontube .having vits control gridconnected to-said fly-back control electrode andrits anode connected to theicontrol grid of said first vacuum tube.

:12. Apparatus :according zto claim 11, in which 'the nanode of;-.said -:,gaseo us conduction :tu-be Eis :also :connected to the control grid of :said second vacuum tube.

13. Apparatus according "to =claim *8, [in which ,:said horizontal fiy-back control electrode-is biassed to produce a negative pulse in response to the impingement thereon'ofsaid beam,- anda pulse inverteris PIOVldCdifOI' inverting said negative :pnlse into a positive'pulse 'before applying it to thecontrol grid :ofsaidtfirst va'cuum tube.

14. Pulse counting apparatus, comprising iamathoderay tube having means :to develop :a :focussed zelectron beam, a targetihaving target-elements-in successive'hoi'izontal rows, a-pair of *horizontal -beam deflector plates, 21 pair of vertical ibeam -deflectonplates, vatfirst vacuum tube amplifier having its output connectedito isaid horizontal plates, a-second vacuum tube amplifier having its "fiy back electrode IO [develop a horizontal -fiyback voltage, means to derive from said horizontal fly back-zvoltage a vertical beam-stepping volt-age, and rmeansito apply said vertical beam-steppingvoltage to :said vertical-plates to step'the beam to the-next hor'izontal row-of-target elements.

15. Pulse 1 counting apparatus according to claim '14,=in

which :vertical and horizontal holding ielectro'des mare: provided-upon which the beam impinges=to:develop ;a beamholding voltage to'hold the'beam on theaparticular target :element to WhlCh it has -been-stepped.

-16. Pulse counting apparatus --according to --cl-aim :15, in which the vertical beam-holding-electrode:is connect d to .the input of said first amplifier, wand the :horizontal beam-holding electrode is connected to the 5 input :of 2 said second amplifier.

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